Number normalization is used in telecommunications networks for receiving a string of dialed numbers from a user and converting the string into a format that can be used by call processing equipment, to route communication sessions from the user to a destination entity. Number normalization is typically used in conjunction with a conventional numbering scheme, such as E.164, recommended by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T), which defines the international public telecommunication numbering plan used in the public switched telephone network (PSTN). The North American Numbering Plan (NANP) includes various geographically-bounded numbering plan areas, having numbers defined by a three-digit area code and a seven-digit telephone number for routing calls.
A specific example of number normalization is abbreviated dialing, in which a user can dial a shortened string of digits to connect within a particular service area. For example, for local dialing within an area code, a user can dial 555-1234 and the number is automatically normalized within the network to the NANP number of 425-555-1234. In dialing within a private corporate network, a further abbreviated number can be used (e.g., 51234) and that dialed string is normalized to 425-555-1234, even for corporate users within the network from different geographic locations outside the local numbering plan boundaries.
In mobile communications, a problem can arise when a mobile user is operating outside the user's normal operating area while traveling, since a user's location affects the normalization of the number. For example, a United States user traveling in the United Kingdom (UK) may be unable to complete calls since the local UK phone network uses different number normalization rules to format the dialed string than the rules used by the user's NANP normalized phone. This results in frustration, inconvenience, and a loss in productivity for the user and for the individuals the user needs to contact.
In addition to mobile phones, normalization can also applied be to other types of mobile devices or mobile-capable systems, such as laptop computers that use different address formats, when roaming across numbering plan boundaries. Such address formats can include URIs (uniform resource identifiers) based addresses, which include both email addresses and session initiation protocol (SIP) addresses.